1. Field of the Invention
The present invention relates generally to a strip dual mode filter utilized to filter microwaves in frequency bands ranging from an ultra high frequency (UHF) band to a super high frequency (SHF) band, and more particularly to a strip dual mode filter in which a resonance width of the microwaves is suitably adjusted. Also, the present invention relates to a dual mode multistage filter in which the strip dual mode filters are arranged in series.
2. Description of the Related Art
A half-wave length open end type of strip ring resonating filter has been generally utilized to filter microwaves ranging from the UHF band to the SHF band. Also, a one-wavelength type of strip ring resonating filter has been recently known. In the one-wavelength type of strip ring resonating filter, no open end to reflect the microwaves is required because a line length of the strip ring resonating filter is equivalent to one wavelength of the microwaves. Therefore, the microwaves are efficiently filtered because energy of the microwaves is not lost in the open end.
However, there are many drawbacks in the one-wavelength type of strip ring resonating filter. That is, it is difficult to manufacture a small-sized strip ring resonating filter because a central portion surrounded by the strip ring resonating filter is a dead space.
Therefore, a dual mode filter in which microwaves in two orthogonal modes are resonated and filtered has been recently proposed. The dual mode filter has not yet been put to practical use.